Civil rights lawyers on Monday appealed a federal court ruling in Philadelphia establishing that citizens do not necessarily have a constitutionally protected right to record police activity.

The American Civil Liberties Union of Pennsylvania and local civil rights lawyers filed an appeal with the U.S. Court of Appeals for the Third Circuit on behalf of two Philadelphia residents, one arrested and the other detained, for taking photographs and video of police incidents in the city.

Last month, U.S. District Judge Mark A. Kearney ruled that unless a videographer announces the recording as an act of protest or a challenge to police, officers may stop the recording.

Civil rights lawyers challenged that ruling Monday, saying the public's right to record images of police is well established.

"The freedom to monitor the police without fearing arrest or retaliation is one of the ways we distinguish a free society from a police state," Reggie Shuford, executive director of the ACLU of Pennsylvania, said in a statement. "We hope the court of appeals will make a clear statement that every person has the right to observe and record police in public, irrespective of whether the purpose is to criticize them."

ACLU lawyer Mary Catherine Roper said that while Kearney's ruling did not make it illegal for citizens to video or photograph the police, the language of his opinion should have made it clear that doing so is a First Amendment right.

"These days, you can't not know that the right to record police is absolutely essential," Roper said. "While we have more and more surveillance by the government, there is no doubt that we have a right to watch them as well."

Roper said the right to record police had been affirmed by U.S. appellate courts in Boston, Chicago, and Atlanta.

"What we are hoping is that the Third Circuit says clearly and strongly that you have a right to film the police doing their job," she said.

Deputy City Solicitor John Coyle said the Police Department had a policy of allowing the public to record officers, but a Third Circuit ruling over the constitutionality of such actions would help cement the law.

The cases driving the appeal center on a self-described legal observer who routinely recorded interaction between police and citizens at public protests and was arrested in 2012 outside the Convention Center, and a Temple University junior who was charged with a summary offense for photographing about 20 officers trying to break up a party in 2013.

Coyle said the two were not detained because they were filming officers.